3.8.3Additional lessons
Obtaining Carbon Compounds in Ecosystems — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 93 of 142
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Modes of Nutrition
An organism's mode of nutrition is the way it obtains the organic molecules that fuel respiration and build its tissues.
Autotroph
- Autotroph An organism that builds its own organic molecules from simple inorganic substances such as carbon dioxide, and so acts as a producer.
Photoautotroph
- Photoautotroph Uses light energy to fix carbon dioxide into carbohydrates by photosynthesis;
- examples are green plants, algae and cyanobacteria.
Chemoautotroph
- Chemoautotroph Gets energy from oxidising inorganic chemicals instead of light, which lets it be the producer at deep-sea vents and in caves.
Heterotroph
- Heterotroph Cannot make its own organic molecules and must take in carbon compounds by feeding on other organisms or their remains.
Anabolism
- Anabolism Reactions that build large molecules from small ones, such as an autotroph making proteins and lipids from its sugars.
| Feature | Autotroph | Heterotroph |
|---|---|---|
| Source of carbon | Inorganic CO₂ | Organic molecules from other organisms |
| Energy source | Light or chemical oxidation | Chemical energy in food |
| Role in food chain | Producer | Consumer, detritivore or saprotroph |
Part 2 of 4Kinds of Heterotroph
Kinds of Heterotroph
Consumer
- Consumer Ingests living or freshly killed organisms and digests them inside its body, passing carbon compounds up the food chain.
Detritivore
- Detritivore Eats dead organic matter and faeces, physically breaking it into smaller pieces;
- earthworms and woodlice are examples.
Saprotroph
- Saprotroph Secretes digestive enzymes onto dead material and absorbs the products;
- many fungi and bacteria feed this way.
Decomposer role
- Decomposer role Detritivores and saprotrophs together release inorganic nutrients from dead tissue so that producers can absorb them again.
Part 3 of 4From Carbon Compounds to Energy
Both autotrophs and heterotrophs respire, so every living organism oxidises carbon compounds to obtain usable energy.
1
Producers fix carbon dioxide into glucose, lipids and amino acids, locking chemical energy into their tissues.
2
Heterotrophs ingest these compounds, digest them and either build new tissue or use them as fuel.
3
Cell respiration oxidises glucose, releasing energy that is transferred to ATP for the life processes of the cell.
4
A fraction of the released energy escapes as heat, which is a by-product of every respiring organism.
5
When organisms die or produce waste, decomposers break down the remaining compounds and return nutrients to the soil.
Part 4 of 4Exam Checklist & Tips
3.8.3 – Key Points for the Exam
- Autotroph An organism that synthesises its own organic molecules from inorganic raw materials.
- Heterotroph An organism that obtains organic molecules by consuming other organisms or their remains.
- Chemoautotroph An autotroph that uses energy from oxidising inorganic chemicals rather than light.
- Saprotroph A heterotroph that digests dead matter externally using secreted enzymes and then absorbs the products.
- Detritivore A heterotroph that ingests dead organic matter and breaks it into smaller fragments.
Common Mistakes
- Saying that only heterotrophs respire;
- autotrophs such as plants respire all the time as well as photosynthesise.
- Treating chemoautotrophs as consumers; they make their own carbon compounds and are producers.
- Confusing detritivores with saprotrophs;
- detritivores ingest and fragment material while saprotrophs digest it externally.
- Stating that decomposers create energy; they only release the energy already stored in dead tissue.
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